The present invention relates to a three stage switching unit or switching structure and more specifically to such a three stage switching unit that comprises a number of incoming group related conductors connected to an input switching stage or first switching stage, a number of outgoing conductors connected to an output switching stage or second switching stage and an intermediate or between related switching stage or third switching stage, related and connectable between said, as an input circuit and output circuit operating, first and second switching stages.
The present invention is further based on such a three stage switching unit where said incoming conductors and outgoing conductors are adapted to transfer electrical information-carrying signals and where a control unit coacts with said switching stages in order to connect one of said incoming conductors with a selected outgoing conductor by means of a connecting path, pointed out through said between related switching stage.
Said input circuits are to present output conductors equipped with electro-optical converters in order to be able to transmit optical pulses, corresponding to a current electrical information-carrying signal, to said between related switching stage and said output circuits presents input conductors equipped with opto-electrical converters in order to receive optical pulses from the between related switching stage corresponding to an information-carrying signal belonging to a current input circuit.
Switching units or switching structures pertaining to this kind with three switching stages has also been denoted a first, second and third switching stage, in a consecutive order, and bearing this in mind it should be noticed that the second switching stage corresponds to the here denoted third switching stage and the third switching stage corresponds to the here denoted second switching stage.
It is, for a man skilled in the art, obvious that such switching units are can handle two-way communication regarding the flow of information but in simplifying purpose the following description will only disclose one selected direction regarding the flow of information.
Multi step switching, pertaining to the kind described above, are previously known in a number of various embodiments and the principal construction and the dimensioning rules concerning a none blocking three stage switching unit are shown and described in more detail in the publication "ISDN and Broadband ISDN" under the section 2:3 "Space-Division Switching" and specifically on page 33 with reference to FIG. 2.8.
The principal construction of a three stage switching unit is here described and dimensioned to be able to provide a none blocking signal transmission at a passage of incoming connections.
The structure of used first, second and third switching stages is not given in detail.
It is, nevertheless, known to form said switching stages so that these are adapted to pass used electrical information-carrying digitized signals, whereby electrical conductors are related to each other and structured according to the pattern indicated by the publication.
Taking the significant features of the present invention under consideration it can also be mentioned that it is previously known to be able to receive electrical information-carrying signals and to, through electro-optical converters, convert these to optical pulses of light and to transmit these light pulses on an optical conductor to an opto-electrical converter which receives said optical pulses and transmits corresponding electrical information-carrying signals.
Such optical information-carrying systems have been used within various electro technical applications, such as large switching units, in order to transmit information-carrying signals longer distances, as in between different or similar cubicles.
Taking the significant features, and thereto significant measures, of the present invention under further consideration it can be mentioned that totally optical switching units are previously known and described through the publication "Technical Digest of Conference on Optical Fiber Communication" in the article "Feasibility demonstration of 2,5 Gbit/s 16.times.16 ATM photonic switching matrix" on pages 93 to 94, by the authors D. Chiaroni et al and the publication "Proc. Topical Meeting on Optical Amplifiers and their Applications, postdeadline paper", 1992, in the article "Monolithically integrated 4.times.4 InGaAsP/InP laser amplifier gate switch arrays" on pages 38 to 42, by the authors M. Gustafsson et al.
In these referred publications it is described the usage of controllable optical switching components, such as optical switching matrixes, whereby optical light pulses, appearing on one of a number of available group related incoming optical conductors, can be selected and switched through a core to a, one of several available, selected outgoing optical conductor.
In order to simplify the understanding of the features if the present invention a reference to the publication "Proc. European Conference on Optical Communication", 1990, with the article "Characterization of a 1,5 m three-electrode DFB laser" on pages 279 to 282, by the authors R.J.S. Pedersen et al, can be made where it is described a tunable laser related transmitter.
A receiver in a laser related application is described in the publication "Proc. European Conference on Optical Communication", 1991, with the article "Performance of DBR active filters in 2.4 Gb/s systems" on pages 445 to 448, by the authors O. Sahlen et al.
The principles of said transmitter and receiver can be used within the present invention.
That which is shown and described in the following publication is also a part of the related art.
"Wavelength Conversion Laser Diodes Application to Wavelength-Division Photonic Cross-Connect Node with Multistage Configuration" H. Rokugawa et al. IEICE Trans. on Communication, Vol. E75-B, No. 4, April 1992, pages 267 - 274.
A three stage switching structure or unit is, through this publication, previously known with a principle construction that coincides with the basic conditions of the present invention.
It is here indicated (according to FIG. 1) the use of an opto-electrical signal converting stage (O/E), a stage intended to process electrical signals (ESP), an electro-optical signal converting stage (E/O), a switching stage adapted to optical signals (OSP), an opto-electrical signal converting stage (O/E), a stage intended to process electrical signals (ESP) and an electro-optical signal converting stage (E/O).
An connecting arrangement for the switching stage (OSP) is described in principal with reference to FIG. 2 which is specifically adapted to a wavelength separation , so that signals with different wavelengths can pass simultaneously through one single optical fiber and the conditions to increase the flexibility and capacity of such an optical communication network has thereby been created.
It can be specifically mentioned that the switching stages used here are dimensioned for one and the same capacity and that the optical switching stage (OSP) is dimensioned and adapted to the O/E- and E/O-stages.
The switching unit is thus dimensioned and adapted to a selected capacity and the possibilities to a gradual extension is neither indicated or mentioned.
It is further made clear, through that which is described in FIG. 2, that all outputs are connected to all inputs through the used optical stage.
It is besides this described possibilities to let a selected wavelength from every selected source (1.1-1.n) to an incoming block to be mixed before an optical signal with several wavelengths (p.sub.l -p.sub.n) is transmitted through an outgoing block.
A separation of wavelengths is thus performed here to a number of possible receivers.
A requirement on an optical switching unit of this kind is that the selected light intensity of the information-carrying signals appearing on one of the inputs must be high enough to be sufficient to all the outputs. "Trend of Photonic Switching Systems" S. Suzuki et al. IEICE, Trans. on Communication, Vol. E75-B, No. 4, April 1992, pages 235-242.
It is here described a number of switching units, intended to be able to transmit broadband signals.
The switching structure according to FIG. 15 can be regarded as being of a certain importance.
It is here described a switching equipment adapted to ATM-cells where the ATM-cells intended to pass through are connected or a multiplexing unit (MUX S/P) which restructure incoming parallel related ATM-cells to a serial related ATM-cell structure on one single conductor and these serial related ATM-cells can be stored within a memory.
Every ATM-cell, regardless of required bandwidth, is now to pass through the optical matrix connection OSM which requires a high speed, meaning that a speed corresponding to ATM-technology is here required through the complete connecting system.
A control of the OSM-stage is required so that, for every ATM-cell that is to pass through the OSM-stage, a selected input connection can be connected with a selected output connection.
Taking the related art, as described above, under consideration it ought to be regarded as a technical problem to be able to create a three stage switching unit with a first, a second and a third switching stage, of the kind that has previously been described, and where the incoming conductors and outgoing conductors are to be adapted to transfer electrical information-carrying digitized signals with a high speed, under the conditions that the between related or third switching stage requires small space and is simple, and to thereby realize that there is a solution in structuring respective switching stage into a number of switching units or switching components.
Besides this it ought to be regarded as a technical problem to be able to realize the importance of selecting the number of output connections of every switching unit within the first switching stage to correspond with the number of switching units within the third switching stage.
It is thereby a technical problem to be able to realize the importance of letting, and the advantages obtained as, every switching unit within the third switching stage is given the same amount of input connections as output connections.
It ought to be, besides this, regarded as a technical problem to be able to realize the simplifications that are provided as the switching units of said between related switching stages can be permitted to be totally opto related regarding receiving, directing and transmitting digitized information-carrying signals without the need of any signals to be converted into electrically related information transmission.
There is a technical problem in being able to realize the savings in the switching structure that can be made by letting every outgoing optical conductor, belonging to an optical switching unit, be supplied with a optical signals distributing unit, a unit that divides an optical signal into two equivalent parts (optical split), where the outgoing conductors of the unit, transferring the same optical pulses, thereby can be connected to one input connection or opto-electrical converter each for every switching unit within the second switching stage.
It must also be regarded as a technical problem to, with a three stage switching unit of the above described kind, be able to realize the importance of, and conditions required to, let every switching unit, within the between related switching stage, be arranged to be able to receive optical signals directly from each and every one of a number of group related incoming optical conductors and to directly be able to connect optical pulses appearing on an incoming conductor, by means of a control signal generated by a control unit, to one of several available selected outgoing optical conductor and that thereby said control unit generates control signals adapted to the used switching units within the first and second switching stages.
It must also be regarded as a technical problem to be able to realize the advantages that are obtained as within a three stage switching unit it can be permitted that every optical pulse to every switching unit within the third switching stage can be passed on as a transmitted optical pulse, without the need of, for these purposes, amplifying circuits for optical pulses.
It must also be regarded to be a technical problem to be able to realize the advantages that can be provided by a three stage switching unit as incoming and outgoing conductors, intended to be used for electrical signals, transfers group related electrical information-carrying signals, structured into data packets, specifically as ATM cells.
There is a technical problem in being able to realize the advantages that are obtained as several data packets, for instance two, given different addresses, can be transferred on the same optical conductor and to adapt an address evaluating circuit, belonging to a receiver, to decide on which of the address related packages that are to be taken care of and which that are to be disposed of and to thereby provide a use of an optical conductor to transfer two additional separate information-carrying digitized signals.
It must also be regarded to be a technical problem to be able to realize and how to accomplish a three stage switching unit that can provide a safe function and a reliable adaption even when the switching units within a first switching stage, structured as an input circuit, are adapted to a total maximum bit rate of more than 50 Gb/s and specifically more than 80 Gb/s.
It must also be regarded as a technical problem to be able to realize the advantages that are obtained by using a control unit which is arranged to activate a connecting path, between a selected input circuit and a selected output circuit through one of said switching units within the third switching stage, which fulfils the required bandwidth depending on the required bandwidth of a connection currently needed by a caller and taking into consideration the selection of one or several wavelengths.
There is also a technical problem in being able to realize the importance of the simplifications that can be expected by letting said control unit control a wavelength selecting unit, belonging to every electro-optical converter of every outgoing conductor from the switching units within the first switching stage, so that the control unit, through said circuit, can select to transmit optical pulses with a first frequency or wavelength or to be adapted to transmit optical pulses of an other frequency or wavelength and at the same time be able to create the conditions that are required to activate receiving circuits, belonging to one or several incoming conductors of output circuits in the switching units, through the control unit, and to thereby provide a usage of an optical conductor for the transmission of two separate information-carrying digitized signals.